When I've found myself being anxious over a topic, it has usually boiled down to either my self confidence or my self worth being a bit shaky. This is normal, and it happens to all of us at times. I've found it to be very helpful to notice what's going on, admit it, and then tend to it by taking action to build up my belief again. To be honest, it has been really interesting to understand the difference between self confidence and self worth because then I'm better able to tell which area needs the boost. Let's look at them both and see what helps.
Self confidence is a trust in your abilities. It's not necessary that you have a high sense of self confidence in all areas, as you're probably strong at some things and less able at, eg, long division. It is, however, important to have a strong self belief in your abilities in the areas that matter to you. Self worth is "a feeling that you are a good person who deserves to be treated with respect" (Merriam-Webster definition). You have a deep knowing that you are a valuable person irrespective of your mathematical or other abilities. You are just as worthy as anyone else on the planet.
Building up your self worth is a practice. When it's low, a combination of self awareness and mindfulness can build it up. Thankfully it's very teachable. See this article and this one. To build up your self confidence you almost have to start proving to yourself that you are capable in that specific area. You have to take a different kind of action.
If I want to be a confident speaker, a huge part of this comes down to my preparation of the speech weeks (months) in advance of actually speaking. I write it early because the first version always needs to be put away and edited two days later with fresh eyes. Then I add more, and practice and practice and practice. I know I'm going to be fine on the day of the talk, because I've put in the weeks rehearsing it. Before I share the talk with anyone, I've already shown myself that it's ready to be shared. The same is true of any presentation, school exam, or interview. You feel much better when you prepare early. Maybe you won't anticipate everything, yet you know you've done your best and because of your preparation you can trust in your abilities to figure the rest out.
There can be areas in which you find you're constantly negative about yourself. You'll put yourself down either overtly or in your mind. That's not going to help you believe in your ability to improve and grow. Instead you need to be your own best coach. If something doesn't go as you hoped, see if you can adopt a "thank goodness it wasn't worse" mindset. When things go well it's useful to note them down either in a small journal or note-taking app. We tend to forget the good things more quickly, so it's helpful to have a running list. I'm grateful that my partner doesn't worry about things that I think "oh no" about. I overcooked something the other night and thought, "that's terrible" and he reflected to me, "it's actually ok." I laughed and realised how seriously I was taking it. Would it matter in a week? No. Can you notice when you're being too serious about something? Can you take the sentence you're telling yourself and reverse it? There are things in life that are terrible, and an over-cooked dinner isn't one of them.
Think of someone you know who has a lovely confidence about them. How to do they stand? How do they enter a room? Can you see through their eyes the way they see things and try to embody their behaviour on a literal level? Stand as they would. Greet people as they would. See if you notice your posture slouching and gently correct yourself. This alone has worked for many people as we often learn by emulating those we admire. It works for confidence too.
Here you'll find essays and musings on applied mindfulness. What does this look like on a daily basis? How can you infuse it in your day to enjoy yourself more? Join hundreds of others on the the mailing list (link in footer) to get these straight to your inbox.